1. Field of the Invention
This invention relates generally to semiconductor fabrication technology, and, more particularly, to a method for manufacturing a workpiece.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably. These demands have resulted in a continual improvement in the manufacture of semiconductor devices, e.g., transistors, as well as in the manufacture of integrated circuit devices incorporating such transistors. Additionally, reducing the defects in the manufacture of the components of a typical transistor also lowers the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
The technologies underlying semiconductor processing tools have attracted increased attention over the last several years, resulting in substantial refinements. However, despite the advances made in this area, many of the processing tools that are currently commercially available suffer certain deficiencies. In particular, such tools often lack advanced process data monitoring capabilities, such as the ability to provide historical parametric data in a user-friendly format, as well as event logging, real-time graphical display of both current processing parameters and the processing parameters of the entire run, and remote, i.e., local site and worldwide, monitoring. These deficiencies can engender nonoptimal control of critical processing parameters, such as throughput accuracy, stability and repeatability, processing temperatures, mechanical tool parameters, and the like. This variability manifests itself as within-run disparities, run-to-run disparities and tool-to-tool disparities that can propagate into deviations in product quality and performance, whereas an ideal monitoring and diagnostics system for such tools would provide a means of monitoring this variability, as well as providing means for optimizing control of critical parameters.
Among the parameters it would be useful to monitor and control are the field oxide (FOX) thickness and the residual FOX defect count following a nitride stripping and/or etching process step. As consecutive lots of workpieces (such as silicon wafers with various process layers formed thereon) are processed through a nitride stripping and/or etching process step, increasing silicon (Si) concentration in the stripping and/or etching bath causes the FOX also to etch in varying amounts. For example, when hot aqueous phosphoric acid (H3PO4) is used to selectively etch silicon nitride (Si3N4), the Si3N4 etches away fairly steadily, at roughly ten times the initial etch rate of the FOX (SiO2). However, when the H3PO4 bath is fresh and the Si concentration is relatively low, the initial etch rate of the FOX (SiO2) is much faster than the later etch rate of the FOX (SiO2), as the H3PO4 bath ages and the Si concentration increases. This causes the FOX thicknesses to increase with time, as the H3PO4 bath ages and the Si concentration increases. In particular, the FOX thicknesses typically vary from run to run and/or batch to batch, leading to varying device performance and an increased number of residual FOX defects, lowering the workpiece throughput and increasing the workpiece manufacturing costs. In addition, if the Si concentration oversaturates, Si may precipitate, contaminating the workpiece(s) and increasing the number of defects.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, a method is provided for manufacturing, the method including processing a first workpiece in a nitride processing step and measuring a thickness of a field oxide feature formed on the first workpiece. The method also includes forming an output signal corresponding to the thickness of the field oxide feature. In addition, the method includes feeding back a control signal based on the output signal to adjust processing performed on a second workpiece in the nitride processing step to adjust a thickness of a field oxide feature formed on the second workpiece toward at least a predetermined threshold value.
In another aspect of the present invention, a computer-readable, program storage device is provided, encoded with instructions that, when executed by a computer, perform a method for manufacturing a workpiece, the method including processing a first workpiece in a nitride processing step and measuring a thickness of a field oxide feature formed on the first workpiece. The method also includes forming an output signal corresponding to the thickness of the field oxide feature. In addition, the method includes feeding back a control signal based on the output signal to adjust processing performed on a second workpiece in the nitride processing step to adjust a thickness of a field oxide feature formed on the second workpiece toward at least a predetermined threshold value.
In yet another aspect of the present invention, a computer programmed to perform a method of manufacturing is provided, the method including processing a first workpiece in a nitride processing step and measuring a thickness of a field oxide feature formed on the first workpiece. The method also includes forming an output signal corresponding to the thickness of the field oxide feature. In addition, the method includes feeding back a control signal based on the output signal to adjust processing performed on a second workpiece in the nitride processing step to adjust a thickness of a field oxide feature formed on the second workpiece toward at least a predetermined threshold value.